Radio Frequency Identification (RF ID) is just one of many identification technologies for identifying objects. The heart of the RF ID system lies in an information carrying tag. The tag functions in response to a coded RF signal received from a base station. Typically, the tag reflects the incident RF carrier back to the base station. Information is transferred as the reflected signal is modulated by the tag according to its programmed information protocol.
The tag consists of a semiconductor chip having RF circuits, logic, and memory. The tag also has an antenna, often a collection of discrete components, capacitors and diodes, for example, a battery in the case of active tags, a substrate for mounting the components, interconnections between components, and a means of physical enclosure. One variety of tag, passive tags, has no battery. They derive their energy from the RF signal used to interrogate the tag. In general, RF ID tags are manufactured by mounting the individual elements to a circuit card.
Basically, passive RF tags consist of two basic parts:
a) An analog circuit which detects and decodes the RF signal and also provides power to the digital part of the Tag using RF field strength from the Base Station, and
b) A digital circuit which implements the multiple items of the tag identification protocol.
A radio frequency (RF) identification system also consists of an RF base station and a plurality of RF tags.
In a typical configuration, the base station has a computer section which issues commands to an RF transmitter and receives commands from the RF receiver. The commands serve to identify tags present in the RF field of the base station.
In some implementations, commands exist to gather information from the tags. In more advance systems, commands exist which output information to the tags. This output information may be held temporarily on the tag, it may remain until over written, or it may remain permanently on the tag.
The RF transmitter of the base station encodes the command from the computer section, modulates it from a base band to the radio frequency, amplifies it, and passes it to the RF antenna. The RF receiver gathers the return signal from the antenna, demodulates it from the RF frequency to the base band, decodes it, and passes it back to the computer section for processing. The base station antenna sends RF signals to and receives RF signals from one or more tags with in the RF signal range.
While the application of RF ID technology is not as widespread as other ID technologies, bar code for example, RF ID is on its way to becoming a pervasive technology in some areas, notably vehicle identification.
Multiple objects can be identified by checking each individually using bar code reader. However, this process consumes a lot of time. It is also error prone--the error rate made by either human beings or by the bar code reader is very high.
This iterative process can be simplified and solved by introducing the RFID Tag technology. The RFID tag can be used to identify multiple objects in a very short time, on the order of a second.
One way of implementing multiple RF tag identification is as follows:
a. the tag powers up in the RF field, starts a clock, and seeds a random number generator.
b. the tag sends out a 64-bit ID (at internal clock frequency) at intervals determined by the random number generator
c. the base station synchronizes to the tag transmission from a transmitting tag in the field. If there is a successful reception (no errors), the station uses a power interrupting to transmit a simple shutdown code to the tag. This approach works because the station is synchronized to that tag and times its shutdown code using that tag frequency. The tag uses the gap detection circuitry to identify power interruptions.
d. Two shutdown modes are available: i) the tag is prevented from talking as long as it remains in the field; and ii) the tag is prevented from talking even after departing field (for approximately 10 minutes or more.) The shutdown mode (ii) is accessible only after shutdown mode (i) has been entered.
e. In this application, multiple items are identified by shutting down each tag immediately after a successful read. Other tags in the field, ideally, will not be synched to the internal frequency of the tag which has just been read, nor, ideally, will they have just finished transmitting their id when the base stations sends the shutdown signal to the tag which has just been identified.
This technology only applies identifying tags only, i.e., there is only a single read channel. The system can not write to the tags.